Forming resistive random access memories together with fuse arrays

ABSTRACT

A resistive random access memory array may be formed on the same substrate with a fuse array. The random access memory and the fuse array may use the same active material. For example, both the fuse array and the memory array may use a chalcogenide material as the active switching material. The main array may use a pattern of perpendicular sets of trench isolations and the fuse array may only use one set of parallel trench isolations. As a result, the fuse array may have a conductive line extending continuously between adjacent trench isolations. In some embodiments, this continuous line may reduce the resistance of the conductive path through the fuses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 14/738,453, filed Jun. 12, 2015, which is a divisional of U.S.patent application Ser. No. 14/066,308 filed Oct. 29, 2013, and issuedas U.S. Pat. No. 9,136,471 on Sep. 15, 2015, which is a continuation ofU.S. patent application Ser. No. 12/849,864 filed on Aug. 4, 2010, andissued as U.S. Pat. No. 8,569,734 on Oct. 29, 2013. The aforementionedapplications and patents are incorporated herein by reference, in theirentirety, and for any purpose.

BACKGROUND

This relates generally to resistive random access memories (ReRAMs).

ReRAM relies on materials that can be electrically switched between ahigher conductive state and a lower conductive state several times. Onetype of ReRAM, a phase change memory, uses phase change materials, i.e.;materials that may be electrically switched between a generallyamorphous and a generally crystalline state. One type of phase changememory element utilizes a phase change material that may be, in oneapplication, electrically switched between a structural state ofgenerally amorphous and generally crystalline local order or betweendifferent detectable states of local order across the entire spectrumbetween completely amorphous and completely crystalline states.

One time programmable fuses may be used in conjunction with a phasechange memory array. For example, fuses may be programmed permanently tostore information which should not be changed. This infom1ation mayinclude trimming values set during manufacture, microcode, andredundancy addresses to replace defective memory elements withreplacement memory elements, to mention a few examples.

The easiest solution to heat fuses in conjunction with the phase changememory array is to permanently blow a phase change storage element. Thiscan be done with high current pulses delivered to the phase changememory cell in reverse polarity.

Because it operates differently, the fuse array must include structuraldifferences over the phase change memory elements. In particular, thereverse polarity and the high current for blowing fuses results inspecific drivers and layout. As a result, the fabrication complexity maybe increased by the inclusion of a fuse array on the same die with amemory array.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, perspective view of a main array in accordancewith one embodiment of the present invention;

FIG. 2 is an enlarged, perspective view of a fuse array in accordancewith one embodiment of the present invention;

FIG. 3 is a cross-section through the main array taken generally alongthe line 3-3 in FIG. 1 taken along the row or wordline;

FIG. 4 is an enlarged, cross-sectional view taken generally along theline 4-4 in FIG. 1;

FIG. 5 is an enlarged, cross-sectional view at a subsequent stage tothat shown in FIG. 3 in accordance with one embodiment;

FIG. 6 is an enlarged, cross-sectional view corresponding to FIG. 4 at asubsequent stage in accordance with one embodiment;

FIG. 7 is an enlarged, cross-sectional view at a subsequent stagecorresponding to FIG. 5 in accordance with one embodiment;

FIG. 8 is an enlarged, cross-sectional view at a subsequent stagecorresponding to FIG. 6 in accordance with one embodiment;

FIG. 9 is an enlarged, cross-sectional view at a subsequent stage tothat shown in FIG. 7 in accordance with one embodiment;

FIG. 10 is an enlarged, cross-sectional view at a subsequent stage tothat shown in FIG. 8 in accordance with one embodiment;

FIG. 11 is an enlarged, cross-sectional view at a subsequent stage tothat shown in FIG. 9 in one embodiment;

FIG. 12 is an enlarged, cross-sectional view at a subsequent stage tothat shown in FIG. 10 in one embodiment;

FIG. 13 is a perspective view at a subsequent stage to that shown inFIG. 1 in accordance with one embodiment;

FIG. 14 is an enlarged, perspective view at a subsequent stage to thatshown in FIG. 2 in accordance with one embodiment;

FIG. 15 is an enlarged, cross-sectional view at a stage subsequent thatshown in FIG. 9 in accordance with one embodiment;

FIG. 16 is an enlarged, cross-sectional view at a stage subsequent tothat shown in FIG. 12 in accordance with one embodiment;

FIG. 17 is an enlarged, cross-sectional view at a stage subsequent tothat shown in FIG. 15 in accordance with one embodiment;

FIG. 18 is an enlarged, cross-sectional view corresponding to FIG. 16 ata subsequent stage in accordance with one embodiment;

FIG. 19 is an enlarged, perspective view of the main array in accordancewith one embodiment at a stage subsequent to that shown in FIG. 14;

FIG. 20 is an enlarged, perspective view at a stage subsequent to thatshown in FIG. 14 in accordance with one embodiment;

FIG. 21 is an enlarged, top plan view of the isolation structures forthe main array (on the left) and the fuse array (on the right) inaccordance with one embodiment;

FIG. 22 is an enlarged, cross-sectional view showing the heaterdeposition according to one embodiment;

FIG. 23 is an enlarged, cross-sectional view showing the heater etchingaccording to one embodiment;

FIG. 24 is a more enlarged, partial top plan view at the main array inaccordance with one embodiment at an early stage of manufacture;

FIG. 25 is a more enlarged, top plan view showing strips that may bepatterned to ultimately form heaters of the main array in accordancewith one embodiment, at a subsequent stage to that shown in FIG. 24;

FIG. 26 is an enlarged, top plan view of the fuse array at the stage ofmanufacture also shown in FIG. 25, in accordance with one embodiment;

FIG. 27 is a greatly enlarged, perspective view of the main array at asubsequent stage in accordance with one embodiment;

FIG. 28 is a greatly enlarged, perspective view of the fuse array inaccordance with some embodiments of the present invention; and

FIG. 29 is a schematic depiction for one embodiment of the presentinvention.

DETAILED DESCRIPTION

A main resistive random access memory array (FIG. 1) and a fuse array(FIG. 2) may be formed using the same or substantially the same steps onthe same semiconductor substrate. Referring to FIG. 1, the semiconductorsubstrate 70 may have a P-type collector 72 in one embodiment. Over theP-type collector 72 may be an N-type base or wordline 74 in oneembodiment. Thus, the wordlines run from left to right in the figure.The bitlines run into the page and include a plurality of P-typeemitters 80. Base contacts 78 separate sets of four emitters in the rowdirection in one embodiment. Thus, deeper trench isolations 82 extend inthe row direction, while shallower trench isolations 84 extend in thebitline direction. While not depicted in FIG. 1, the deeper andshallower trench isolations 82 and 84 may be filled with a dielectric,such as silicon dioxide.

The emitters 80 and base contacts 78 may be formed by ion implantationwith appropriate masking in one embodiment. The mask may be opened toform the appropriate conductivity type at the appropriate locations.Conductivity types other than those described herein may be used. Othertrench depths and orientations are possible in other embodiments.

Referring to FIG. 2, the fuse array may have the same arrangement oftrench isolations 82 and 84 that are formed at the same time, using thesame sequence of semiconductor processing operations, as used to formthe corresponding trenches for the main array shown in FIG. 1, in oneembodiment. As in the main array, the fuse array may also include basecontacts 78. However, the fuse array may include fuse contacts 86instead of emitters. In one embodiment, the base contacts 78 and fusecontacts 86 are N+ doped and may be formed at the same process step.

FIGS. 3-12 and 15-18 show the fabrication of the main array, with theodd numbered figures being row direction cross-sections and the evennumbered figures being cross-sections in the bitline direction. In theillustrated embodiment, the main array is a phase change memory, butother resistive random access memories may also be used.

In FIGS. 3 and 4, a dielectric 88 fills the deeper and shallowertrenches 82 and 84. A silicon nitride layer 90 may be fanned under asilicon oxide layer 92. However, other dielectrics may also be used. Inone embodiment, silicide plus tungsten plugs 94 may be formed above thesilicon regions 78, 80 and 86 and under the silicon nitride layer 90.Note that the same plugs may be used in the main array and the fusearray. Thus, while the dielectric layers 90 and 92 are continuous in therow direction, they are trenched, as seen in the bitline direction inFIG. 4 in one embodiment. Namely, the trenches 96 may nm in the rowdirection, leaving a dielectric layer spanning each pair of two emitters80.

Then, referring to FIGS. 5 and 6, the structures may be covered by amaterial used to form heaters 98. For example, titanium nitridecomposites may be utilized for this purpose. The heaters 98 may coverthe dielectric material and the trenches between the dielectricmaterial, as shown in FIGS. 5 and 6.

Then, as shown in FIGS. 7 and 8, the heater 98 material is removed fromthe tops of the dielectric layers 90 and 92 so that only the upstandingvertical portions remain, as indicated at 98 in FIG. 8. Thus, theL-shaped remnants 98 mn in the row direction. A nitride material 100 maybe deposited over the resulting structure and then trenched, asindicated, to form sidewall spacers shown in FIG. 8.

Then, the structure shown in FIG. 8 may be covered by still anotherdielectric layer 102 which, in one embodiment, may be silicon dioxide,as shown in FIGS. 9 and 10.

Moving to FIG. 11, the structure may be planarized to remove the upperpart of the dielectric layer 102, creating the planar structure shown inFIG. 12. The planarization may go all the way down to the nitride layer90 in one embodiment.

Referring to FIG. 13, the resulting heaters 98 may be L-shaped and mayrun in the row direction. Adjacent rows may have L-shaped heaters 98that face in opposite directions. The heaters 98 are further defined asa result of an ensuing self-aligned etch of a chalcogenide bitline whichactually occurs subsequently in the process flow, but the heaters areshown here to illustrate the L-shape in advance of the chalcogenidebitline etching step. The heaters 98 arc positioned in the main array onthe emitters 80.

FIG. 14 shows the heaters 98 for the fuse array. In this case, theheaters 98 are positioned on top of the fuse contacts 86 with nodifference with respect to the steps employed for the heater formationin the main array as described in FIGS. 3-12. In this case no bipolartransistor is present below the heater and the bottom of the heaterelement is in direct electrical contact with the N-doped silicon pillarsof the base 74.

Continuing with FIG. 15, a series of layers are added including achalcogenide layer 104 in the case of a phase change memory embodiment.The chalcogenide layer 104 may be any material suitable for forming aphase change memory including the so called GST (germanium, antimony,tellurium) material. In some embodiments, over the phase change orchalcogenide layer 104 may be a metallic cap 106 which, in oneembodiment, may be titanium nitride. Next, still another metal layer maybe deposited, as indicated at 108. The layer 108, in one embodiment, maybe tungsten to increase bitline conductivity.

Referring to FIG. 16, the chalcogenide layer 104 makes contact with theheaters 98 at their upper ends.

The bitline definition step involves etching to define the bitlines, asshown in the wordline direction of FIG. 17. The resulting trenches 110nm in the bitline direction and define bitlines 112 running into thepage in FIG. 17 and across the page in FIG. 18, which is the bitlinedirection. This is the self-aligned etch of the bitline down to thetungsten plugs 94. A larger opening 114 is formed over the base contacts78.

Referring to FIG. 19, overlying layers have been removed in theperspective depiction to show the arrangement of the chalcogenide layers104. As shown there, the chalcogenide layers extend only over theemitters 80 and make contact with the now singulated heaters 98. Notethat the heaters were singulated during the self-aligned bitline etch.Thus, the chalcogenide layers run in the bitline direction, as indicatedin FIG. 19.

FIG. 20 shows the corresponding structure in the fuse array. Note thatin the fuse array, there is a partial self-aligned bitline etch whichleaves only portions of the chalcogenide layer 104 along a firstwordline at the edge of the array.

Thereafter, conventional steps may be utilized to form copper damascenelines in the row and bitline directions on the fuse and main arrays insome embodiments.

In accordance with another embodiment, a resistive random access memory(ReRAM) main array and fuse array may be made on the same siliconsubstrate. In some embodiments, process complexity may be reduced andefficiencies may be achieved by using similar processing techniques forboth the fuse array and the main array, despite the structuraldifferences between the two arrays. In addition, it is advantageous toform only one fuse per bitline in accordance with some embodiments wherethe selecting transistor is realized at the array edge. The missingfuses on each bitline then provide spacing between adjacent fuses, whichmay reduce shorts or damage when fuses are blown, in some embodiments.

In some cases, the word lines may be tied together. A vector arrangementmay use common word lines, with fuses driven by drivers along the edgeof the fuse array rather than drivers under the fuses. As a result, therow parasitic resistance of each fuse may be reduced, improvingperformance in some embodiments.

Referring to FIG. 21, the main array, including the ReRAM cells, mayinclude spaced, parallel, shallower trench isolations 14 andperpendicular spaced, parallel, deeper isolations 16 a. The isolations14 or 16 a may be in the form of trenches in a semiconductor substrate,those trenches being filled with a dielectric. A cell active area may bedefined at the intersection between two adjacent deeper trenchisolations 16a and between two adjacent shallower trench isolations 14.Below each cell active area 23 may be a select transistor (not shown inFIG. 21) in the form of a bipolar junction transistor in one embodiment.A resistive random access memory element may be formed directly over theselect transistor, in some embodiments. That is, in some embodiments,each ReRAM cell includes its own underlying select transistor. Othermain array configurations may also be used.

In the fuse array 12, shown on the right side in FIG. 21, there is onlyone set of spaced, parallel trench isolations 16 b. The trenchisolations 16 b correspond to the shallower trench isolations 16 a inthe main array. However, the perpendicular trench isolations 14 may beomitted in the fuse array and, instead, the fuse array may include wordlines 18 that extend continuously between adjacent trench isolations 16b. Thus, in contrast to the main array, the fuse array uses continuousword lines that simultaneously drive many fuse cells along a row forexample, while the main array includes a series of individual bipolarjunction transistors that drive each cell, in some embodiments.

Advantageously, in some embodiments, the use of continuous, lowresistance word lines may reduce the parasitic resistance of the fusearray. The resistance may be important in the fuse array because of theneed for relatively high currents to destructively program the fuses inthe fuse array. In some embodiments, the fuses may be programmed bypassing a reverse biased high current through them, causing destructivefailure. As a result, the fuses are either unprogrammed or programmed bycausing the fuses to fail by the passage of relatively high current. Inone embodiment, the word lines 14 may be formed of silicide such ascobalt silicide, fomled on top of the same semiconductor substrate inwhich the trenches were formed.

Then, in FIG. 22, a heater layer 20 and, optionally, a dielectric sheathlayer 126, both having sublithographic thickness, are conformallydeposited on the wafer 100. The heater layer 20 may constitute aplurality of parallel, spaced strips running in the bitline directionindicated as “Y” in FIG. 22. In a phase change memory embodiment, thestrips 20 may be formed of a heater material. For example, the heatermaterial may produce Joule heat in response to current flow. Inembodiments using non-phase change resistive random access memories and,in some phase change memory embodiments, the heater material may bereplaced by corresponding strips of conductive material and, in somecases, no heater may be used. The same masks may be used to produce thestrips in the fuse array and the main array. The thickness of the heaterlayer 20 may be in the range of 5-20 nm in some embodiments.

The heater layer 20 may be formed over a dielectric layer 18 in whichare formed contacts 24 which, in some embodiments, may be either basecontacts or emitter contacts of a bipolar select transistor. The trench124 in overlying dielectric layers 121 and 122 enables heaters to makean electrical connection to the contacts 24.

The heater layer 20 and the sheath layer 126 are etched back and flatportions thereof are removed from the bottom of the heater trench 124,as illustrated at 127 in FIG. 3. In practice, vertical portions of theheater layer 20 and of the sheath layer 126 adhering to sides of theheater trenches 124 are separated from each other and define heaterstrips 20 and sheath portions 126, respectively, extending in the rowdirection. Therefore, the second dielectric layer 122 outside the heatertrenches 124, and the first dielectric layer 18, the base contacts 24 aand the emitter contacts 24 b inside the heater trenches 124 are exposedagain. The heater strips 20′ are in the form of rectilinear verticalwalls, miming perpendicular to the column direction Y and having smalllateral protrusions at bottom. In practice, two separate heater strips20′ are obtained from the heater layer 20 in each heater trench 124;each of the heater strips 20′ extends on a respective row of selectiontransistors and is isolated from any other heater strips 20 of the wafer52. A filling layer (not shown) is deposited on the wafer 52 and removedfrom outside the heater trenches 124 by chemical mechanicalplanarization. Hence, the heater trenches 124 are tilled by fillingportions 127 of the filling layer, illustrated by a dashed line in FIG.23.

Referring next to FIG. 24, a portion of the main or fuse array is shownat an early stage of fabrication. In each array, an etch mask (notshown) extending in the same direction as the shallow trench isolations16a forms a plurality of parallel, spaced heater strips 20.

Next, a plurality of layers may be built up over the strips 20. For aphase change memory, a phase change material, such as GST, may bedeposited as one of those layers, followed by other suitable layers,including a conductive cap and, in some embodiments, a metal line, suchas a copper metal line. In other resistive memories, a differentswitching material, such as nickel oxide, titanium dioxide, silicondioxide, or MnOx may be used, to mention a few examples.

Then, a mask (not shown) extending perpendicularly to the mask used toform the strips 20′ (shown in FIG. 24), may be used to form theparallel, spaced lines 22 shown in FIG. 25. Thus, the stack of depositedlayers, including a switching material, is etched, leaving theunderlying or masked portions 20 a of the strips 20′ and also defininglines 22 that actually include the switching material for the fuse andmain array cells. The lines 22 extend perpendicularly to the originallengths of strips 20, which now have been segmented into discreteheaters 20 a, each coupled to an external select transistor (not shownin FIG. 23), an underlying heater 20 a in a phase change memoryapplication, and an overlying ReRAM cell (not shown in FIG. 23). Themain array cells 27 may include a chalcogenide in the case of a phasechange memory or a resistive switching material in the case of aresistive random access memory other than a phase change memory. Thus,in the main array, the regular matrix of cells 27 may be formed, eachcell being equidistantly spaced from its adjacent cells in a gridpattern in some embodiments.

Referring to FIG. 26, at the same time, using the same masks used inFIG. 23, a different structure is achieved in the fuse array. In thefuse array, the same depositions arc applied to form the same stack asin the main array, but the depositions are patterned differently in adirection transverse to the length of the lines 22 shown in FIG. 23. Asa result, the lines 22 have different lengths and are interrupted by agap Gin the vertical direction in FIG. 26.

That is, every other line 22 a is longer in the vertical or bitlinedirection than the adjacent lines 22 b on top of the gap G. Below thegap G, the lines 22 c continue the lines 22 a and the lines 22 dcontinue the lines 22 b. Thus, each longer line 22 a on the top isaligned with a shorter line 22 c below the gap G. Likewise, each shorterline 22 b on top is aligned with a longer line 22 d below the gap G.

As a result, cells 26 are only formed where the longer lines 22 a or 22d overlap the heaters 20 a. A complete grid pattern of cells is notachieved in the fuse array because, on alternate lines 22 b and 22 c,fuse cells are not forn1ed. This provides some spacing between theadjacent fuses, which may improve reliability in some embodiments. Thatis, the adjacent neighbors of each existing fuse are removed so thatthere is greater spacing from one fuse to the next.

Moreover, for each line 22 extending in the ve1iical or bitlinedirection, only one fuse 26 is forn1ed in some embodiments.Particularly, as explained in greater detail hereafter, for each of thelines 22 b or 22 c no fuse is formed, but a fuse is formed on theopposite side of the gap G on the opposite side of the fuse array on thelines 22 a and 22 d. As a result, only one fuse is formed per verticalline 22 a/22 c or 22 b/22 d in some embodiments. Each line 22 a/22 c and22 b/22 d may correspond to a bitline in some embodiments.

Moving to FIG. 27, the main array includes the deeper isolations 16 arunning from the left side inwardly, while the shallower isolations 14nm from the right side into the page. A plurality of pillar shapedcontacts 24, which may be tungsten contacts, may connect to silicidedregions 50, segmented by the shallower isolations 14.

Above the contacts 24 may be the heaters 20 a, in a phase change memoryembodiment. The switching material 26, in the case of a phase changememory embodiment, may be a chalcogenide plus an overlying conductivecap in some embodiments. Overlying the switching material 26 is thefirst metallization layer 30 that may be copper, in some embodiments,that forms metal bitlines in some embodiments.

As a result, each main memory cell 27 may be selected by a selecttransistor, including a region 50, formed in the substrate 52. Thismeans that each memory cell 27 in the main array may be individuallyaddressed and accessed from below. However, the cells in each bitlineare continuously formed so they are unsegmented, while segmentationbetween adjacent cells occurs only in the word line direction.

Straps 28, in the form of vertical vias, may connect the selecttransistors in the substrate 52 to the metallization (M2) 32 in someembodiments. The M2 lines 32 are, therefore, removed from the array and,therefore, may be wider (or may be formed by 20 multiple lines),reducing their resistance.

The heaters 20 a are self-aligned to each cell 27 since the heaters 20 aare segmented by the same etch used to segment the bitlines, in someembodiments.

Below the contacts 24, the bipolar select transistors may be segmentedby the perpendicular trenches 14 and 16 a in the substrate 52. Thebipolar select transistors each include a region 50 which may be formedof silicide.

Referring to FIG. 28, in the fuse array, fuse cells 26 a and 26 b aredefined overheaters 20 a. Intermediate between the two cells 26 a and 26b, as indicated by 34, a heater and the overlying portion of the cellare missing. That is, a fuse is missing between two adjacent fuses 26 aand 26 b. This missing fuse and heater were removed by the etch thatfanned the shortened lines 22 b and 22 c shown in FIG. 26. The fuses 26a and 26 b are formed where the longer lines 22 a overlap the heaters 20a, as shown in FIGS. 24 and 26. Similarly, another fuse is missing tothe right of the fuse 26 b in this embodiment, corresponding to theshortened line 22 b in FIG. 26.

In some embodiments, the length of the switching material 26 and thebitline 30 may be the same. In another embodiment, the bitline 30 may becontinuous (unlike what is shown in FIG. 8), while the switchingmaterial is discontinuous, as shown in FIG. 8.

In some embodiments, the silicidation that forms the contacts 50 in themain array also forms the word lines 18 in the fuse array.

An alternating arrangement of fuses is shown in FIG. 29, where only onefuse 26 is formed on each line 22. In some embodiments, a selecttransistor 40 is provided for each fuse along the edge of the fusearray. This means that a select transistor 40 is provided for each line22 a or 22 d on one or the other side of the fuse array. In general, afuse and a transistor 40 for that fuse may be on the same side of thefuse array in some embodiments. As a result, the resistance due to linelength is reduced in some embodiments.

Each fuse cell 26 is coupled to one line 22 and each line 22 has onlyone fuse 26 per line 22 in one embodiment. All of the word lines 18 inthe fuse array are connected to a common bias and include no decoder inone embodiment. Each of the select transistors 40 maybe a NMOStransistor in one embodiment. The gates of the transistors 40 may becoupled to a decoder.

In some embodiments, NMOS transistor selectors 40 can be formed in thefuse array along the edges of the fuse array. This enables the use ofNMOS selectors 40 in the fuse array because they can be fom1ed out fromunder the fuses. At the same time, bipolar junction select transistorscan be fanned under each main array cell.

In some embodiments, the fuse array is much smaller with respect to themain array even though the cell density of the fuse array is lower.Enlarging the size of the fuse array may improve reproducibility in someembodiments.

Programming to alter the state or phase of the material may beaccomplished by applying voltage potentials to bottom and topelectrodes, thereby generating a voltage potential across a memoryelement including a resistive switching material. Considering the caseof phase change memories, when the voltage potential is greater than thethreshold voltages of any select device and memory element, then anelectrical current may flow through a heater and the switching materialin response to the applied voltage potentials, and may result in heatingof the switching material.

This heating may alter the memory state or phase of the switchingmaterial, in one phase change memory embodiment. Altering the phase orstate of the material 16 may alter the electrical characteristic ofmemory material, e.g., the resistance or threshold voltage of thematerial may be altered by altering the phase of the memory material.

In the “reset” state, memory material may be in an amorphous orsemi-amorphous state and in the “set” state, memory material may be in acrystalline or semi-crystalline state. The resistance of memory materialin the amorphous or semi-amorphous state may be greater than theresistance of memory material in the crystalline or semi-crystallinestate. It is to be appreciated that the association of reset and setwith amorphous and crystalline states, respectively, is a convention andthat at least an opposite convention may be adopted.

Using electrical current, memory material may be heated to a relativelyhigher temperature to melt and then quenched to vitrify and “reset”memory material in an amorphous state (e.g., program memory material toa logic “0” value). Heating the volume of memory material to arelatively lower crystallization temperature may crystallize ordevitrify memory material and “set” memory material (e.g., programmemory material to a logic “1” value). Various resistances of memorymaterial may be achieved to store information by varying the amount ofcurrent t1ow and duration through the volume of memory material.

References throughout this specification to “one embodiment” or “anembodiment” mean that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneimplementation encompassed within the present invention. Thus,appearances of the phrase “one embodiment” or “in an embodiment” are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be instituted inother suitable forms other than the particular embodiment illustratedand all such fom1s may be encompassed within the claims of the presentapplication.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed:
 1. An apparatus, comprising: an array of resistivememory elements formed on a substrate, wherein the array includes firstand second sets of parallel trenches, and wherein the second set ofparallel trenches is orthogonal to the first set of parallel trenches;and a fuse array formed on the substrate, wherein the fuse arrayincludes a third set of parallel trenches and a continuous wordlineconfigured to drive one or more cells of the fuse array.
 2. Theapparatus of claim 1, wherein the first set of parallel trenches isshallower than the second set of parallel trenches.
 3. The apparatus ofclaim 1, wherein the one or more cells of the fuse array areprogrammable by a reverse bias current.
 4. The apparatus of claim 3,wherein the reverse bias current causes destructive failure of the oneor more cells in the fuse array.
 5. The apparatus of claim 1, whereinthe third set of trenches define a plurality of address lines of thefuse array; and each cell of the one or more cells of he fuse arraycorresponds to an address line of the plurality of address lines.
 6. Theapparatus of claim 1, wherein each cell of the one or more cells of thefuse array comprises a singulated heater.
 7. The apparatus of claim 1,wherein the array of resistive memory elements and the fuse array areformed on a common die.
 8. An apparatus comprising: a chalcogenidememory array formed on a substrate and having a first set of trenchesand a second set of trenches orthogonal to the first set of trenches; afuse array formed on the substrate and having continuous wordlinesconfigured to drive one or more cells of the fuse array.
 9. Theapparatus of claim 8, wherein the first set of trenches are deeper thanthe second set of trenches.
 10. The apparatus of claim 8, wherein theone or more cells of the fuse array each comprise a fuse contact. 11.The apparatus of claim 8, wherein the continuous wordlines areconfigured to reduce parasitic resistance in the fuse array.
 12. Theapparatus of claim 8, wherein the fuse array is programmable by applyinga reverse biased current to the one or more cells of the fuse array. 13.The apparatus of claim 8, wherein the fuse array further comprises athird set of trenches defining the continuous wordlines.
 14. Theapparatus of claim 13, wherein the third set of enches are extensions ofhe first set of trenches.
 15. A method comprising: forming a first setof trenches having a first depth; forming a second set of trencheshaving a second depth, wherein the second set of trenches isperpendicular to the first set of trenches to define an array ofresistive memory elements; and forming a third set of trenches havingthe first depth to define a fuse array having continuous wordlinesconfigured to drive one or more cells of the fuse array.
 16. The methodof claim 15, wherein each cell in the fuse array comprises a collector,the continuous wordline, a fuse contact, and a cap over the fusecontact.
 17. The method of claim 16, further comprising: forming aheater over at least a portion of the cap for each cell in the fusearray.
 18. The method of claim 17, wherein the heater is L-shaped. 19.The method of claim 18, further comprising: forming a chalcogenide layerover the heater.
 20. The method of claim 19, further comprising: etchingthe chalcogenide layer to leave portions of the chalcogenide layer overonly a first wordline at an edge of the fuse array.